Slewing device for screw caps and method for putting screw caps on containers

ABSTRACT

A slewing device for screw closures for containers includes a screw closure receiving member, a drive for rotating the receiving member, and a control arrangement for controlling power supply to the drive and including a torque sensor for sensing an instantaneous drive torque, a comparator for comparing the instantaneous drive torque with a closing torque having a predetermined value, and a sensor for sensing an angle of rotation of the receiving member and actuatable only upon the instantaneous drive torque reaching the predetermine value. The method of placing a screw closure on a container includes applying a drive torque to the screw closure to screw it down onto the container, sensing an instantaneous drive torque applied to the screw closure, comparing the instantaneous drive torque with a closing torque having a predetermined value, and sensing an angle of rotation of the screw closure only upon the instantaneous drive torque reaching the predetermined value of the closing torque.

BACKGROUND OF THE INVENTION

The invention relates to a slewing device for screw closures, inparticular, from plastic materials, for containers and comprising adrive and a torque limiter for controlling power supply to the drive andincluding a torque sensor and an angle of rotation sensor, and a methodof placing screw closures on containers using the slewing deviceaccording to the invention.

A slewing device for screw caps or screw closures as well as a methodfor putting such closures or caps on containers are known (DE-OS 37 15935). The known slewing mechanism serves for screwing screw caps ontoreceptacles and observe herein a preset closing moment. A torque limiterprevents exceeding the desired moment. For this purpose a controlcircuit measures the drive current absorbed by the drive motor of therotational device and triggers control signals if the current rises to aspecific value corresponding to a specific torque of the threaded-on capor closure, by means of which the drive current of the drive motor isinterrupted. Thus one directly affects the energy supply of the drive.

However it was seen that in some cases especially when using solidplastic closures, a secure sealing of the container is not achievablealso when presetting a specific closure moment. This applies especiallywhen containers or bottles subjected to an overpressure are to beclosed. By presetting a specific closure moment it is in additionpossible to damage the mouth region of the container to be closed,especially with glass bottles, which leads to danger for the consumer.Finally it is seen, that the opening moment, meaning torque required forinitial opening of the container, is often considerably higher thandesired.

It is therefore the task of the invention to create a slewing mechanismas well as a method, by means of which containers with screw closures,especially also those made of plastics material, can be closed, whereincontainers subjected to overpressure are closed in a pressure-tightmanner however without being damaged in the mouth region and where aspecific opening moment is set up.

SUMMARY OF THE INVENTION

This task is solved in a slewing mechanism in which the torque limiterdetermines the angle of rotation only after a predetermined closingtorque is reached. Since the control arrangement or the torque limiterdetermines to begin with by means of a torque sensor whether a specificclosure moment, the application or applied moment, is reached during aclosure process, a defined point of departure or point of reference forthe additional measurement during the closure process is established.After reaching this application moment the angle of rotation isacquired, through which the screw closure is turned by the slewingmechanism. A particularly sensitive closure of the container is assuredby acquisition of the angle of rotation after reaching the applicationmoment. This permits to exclude damage to the mouth area with a highdegree of certainty and to assure a very precise observation of adesired opening moment.

In a preferred embodiment of the slewing mechanism or device the controlarrangement is laid out in such a way, that the angle of rotationthrough which the screw cap or screw closure continues to be turnedafter reaching a predetermined application moment can be limited to apresettable value. This layout of the slewing device results in aparticularly sensitive adjustment of the desired closing moment, whereinthe predetermined opening moment can be observed very accurately.

In a preferred embodiment form of the slewing mechanism the torqueacting upon the screw closure is acquired by means of the controlarrangement serving as torque limiter. Herein the current fed to thedrive or the voltage applied to the drive of the slewing device isregistered. Since the power absorbed by the drive is proportional to thevoltage or to the current, the momentary torque can be determined fromthe momentary value of the current or the voltage. This determination ofthe moment is particularly easy to perform.

In an additional preferred closure mechanism the chronological change ofthe tightening moment is determined or registered. If thus the cap orclosure suddenly hangs up or tilts when being threaded on, which isrecognized by a rapid rise of the moment per unit time, the closureprocess can be broken off, so that the mouth region of the container isnot damaged.

The described task is solved by means of a method in which the screwclosure is screwed down until it reaches a predetermined closing momentand, thereafter, an angle of rotation and/or a chronological change isdetermined. In order to achieve a particularly sensitive control of thedesired closure moment, the cap or closure is to begin with threadedonto the container until a predetermined tightening moment, theapplication moment, has been reached. With this a defined initial stateof the closure process is reached. After this the closure or capcontinues to be turned through a predeterminable angle of rotationrelative to the container. This leads to a secure setup of the desiredclosure moment, wherein damage to the mouth of the container are to allintents and purposes eliminated.

According to a preferred embodiment form of the method the chronologicalchange of the tightening moment is additionally registered after theapplication moment has been reached. Obstructions or troubles in themethod during this phase, for instance tilting of the closure on thecontainer can thus be safely determined.

Finally an embodiment form of the method is preferred, where the screwclosure or cap is threaded on up to attaining a high limiting momentexceeding the closure moment. Subsequently the closure is turned inopposite direction through a predeterminable angle of turn, in order toset up the desired closure moment and with this also a specific openingmoment. It is particularly advantageous in this method that containerswhose threads have minor damage can also be closed; in this case anincreased closure moment must therefore be applied in order to threadthe closure onto the container.

Even if the closure is for instance provided with a safety ring a highertorque must be applied when closing, because the closing moment couldoften already be reached, before the screw closure is in its finalposition. Through the initially selected high limiting moment aparticularly good contact pressure of the seal against the mouth regionof the container is assured, so that minor damage is compensated. Aparticularly good sealing of the container is achieved in this manner.

BRIEF DESCRIPTION OF THE DRAWINGS

Single FIGURE of the drawing shows a schematic view of a slewing deviceaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The drawing shows a container 1, in this case a bottle, on which a screwcap 3 of a plastics material is to be threaded or screwed on. Theclosure or cap is gripped by a sketched closing cone 5 of a slewingdevice 7 and is placed upon the container 1. Herein it is unimportantfor the invention, whether the closing cone 5 is turned with respect tothe container 1, or whether the closure cone remains stationary and thecontainer 1 rotates.

The closure cone 5 is rotated in this case by a motor 9 serving as adrive, which is supplied with current or voltage through a switchingdevice 11. A sensor 13 is provided between the energy supply and theswitching arrangement, which sensor determines the current or thevoltage. Basically it is also possible to provide the sensor 13 betweenthe switching device 11 and the motor 9.

A torque sensor 15 determining the torque is allocated to the motor 9 orthe closure cone 5, which determines or acquires the closure momentacting upon the screw closure 3. In addition an angle of rotation sensor17 is allocated to the closure cone 5, which determines the angularposition of the cone.

An elongation measuring strip system (DMS) integrated into a notexplicitly shown spindle of the motor 5 is preferably used as a torquesensor 15. An opto-electronic incremental transmitter is preferred forangular measurement.

The signals of the current- or voltage-sensor 13, the torque sensor 15and the angle of rotation sensor 17 are fed to a control arrangement 19which evaluates and processes the measured values. In addition thesesignals are fed to a comparator circuit 21. This comparator circuitcontains also values M1, M2, M3, M7, and Mo for predetermined tighteningmoments presettable by suitable actuators as well as specific values Wand W1 for predetermined angles of rotation. The output signals of thecomparator circuit 21 are fed to a control arrangement 19.

The control apparatus 19 is connected by a control line 23 with theswitching device 11 of the motor 9. In addition it is provided with adifferential member 25, to which the output signals of the torque- andangle of rotation sensor are fed.

Sensor 13 registering the supply voltage and/or the supply current ofthe motor 9 serves to determine the torque momentarily generated by themotor, wherein one proceeds from the circumstance that the moment isproportional to the voltage or of the current. By determining thechronological change of the supply voltage or the supply current of themotor the chronological changes of the torque can also be acquired. Inthis case the torque sensor 15, which is described above, could beeliminated.

In the following the mode of operation of the slewing device 7 as wellas the method for closing containers is described in more detail.

Basically the device and the method are suitable for closing any type ofcontainer. The use of the device or the method for closing bottles byplastics caps is preferred. The bottles can herein consist of glass oron their part also of a plastics material, for instance PET.

The screw closure 3 is introduced into the closure cone 5 in any randommanner, for instance by means of a so-called pick method. Subsequentlythe closure cone with the screw closure 3 clamped therein is disposedabove the container 1 which is to be sealed or closed off. Herein inthis case the closure cone 5 rotates relative to the stationarycontainer 1.

The rotating screw closure 1 is now placed upon the container 1. Forthis purpose an appropriate switching signal is issued by the controlarrangement 19 through the control line 23 to the switching device 11comprising for instance an electronic switch or a relay, so that themotor 9 is supplied with energy. During the tightening of the closure 3on the container 1 the closure moment or the tightening moment exertedby the motor 9 upon the closure cone 5 or the screw closure 3 isdetermined. The momentary or instantaneous moment can first of all bedetermined by the sensor 13, which registers the current or the voltagesupply by the energy supplied to the motor 9. It is also possible todetermine the moment transferred from the motor 9 to the closure cone 5by means of a torque sensor 15. The output signal of the sensor 13 orthe torque sensor 15 is directed to the control arrangement 19 howeveralso to the comparator 21. The comparator compares the actual momentaryvalue with a predeterminable tightening moment M1, the so-calledapplication moment. As soon as this moment M1 is reached, the angularrotation sensor 17 is activated by the control device 19. The controldevice 19 now evaluates the signals of the angle of rotation sensor. Theactual angle of rotation of the closure cone 5 or the closure 3 iscompared in the comparator 21 with a predetermined angular value W. Assoon as the closure is additionally screwed down through the desiredangle of rotation W after reaching the application moment M1, thecontrol device 19 issues a signal to the switching arrangement 11through the line 23, so that said switching arrangement interrupts theenergy supply to the motor 9. Thus a further turning of the closure isprevented.

If the current- or voltage sensor 13 is utilized, the angle of rotationsensor 17 can be eliminated. The moment supplied by the motor 9 can bedetermined in such an accurate manner, that the switching arrangement 11is actuated in such a way through the control arrangement 19 and thecontrol line 23, that the motor 9 is switched off. In a DC motor thetorque is proportional to the current or voltage applied to the motor.If only a lower accuracy is desired when reaching the closure moment M2,this method of closing containers is adequate.

If the application moment M1 or the closure moment are not reached, thenthe following conclusion can be drawn therefrom:

The closure or cap has dropped out of the closure cone prior to reachingthe container, no container has been moved beneath the closure cone dueto a control error or however the thread of the container or theinternal thread of the closure is ruined.

The control arrangement 19 can for instance be provided with a timingmember, which presets a specific time within which the application- orthe closure moment must have been reached. If this is not the case, acontrol signal is issued through a signal line S and the container 1momentarily arranged beneath the closure cone 5 is removed from theclosing installation.

Instead of presetting a specific time period, which is allowed at themost to elapse before the application moment M1 is reached, a specificangle of rotation can also be preset. This means the closure is forinstance threaded onto the container through a complete revolution.After that the application moment must have been reached. Should thisnot be the case then one deduces therefrom that damage is present at thecontainer or the closure cap. This particular container is then removed.

If however on the other hand the application moment M1 is reached andthe angular rotation sensor 17 has been activated by the controlarrangement 19, the closure cone 5 is rotated further, until themomentary angle of rotation reaches the value W entered into thecomparator 21. The predetermined angle of rotation W is fixed as aresult of tests. Thus it is assured, that the desired closure moment M2is reached. It is on the one hand assured with such a predeterminedclosure moment, that the container is closed or sealed by the screwclosure 3 in a pressure-tight manner. On the other hand it assures thatthe opening moment Mo required for initially opening the container isalso adhered to.

While the screw closure 3 continues to be turned through thepredetermined angle of rotation W, the momentary tightening moment cancontinue to be monitored by the torque sensor 15 and to be compared inthe comparator circuit 21 with a second moment value, a predeterminedmaximum value of M3. If this maximum value M3 is attained during furtherturning of the closure, then one can deduce that a defective mouth ofthe bottle exists. If for instance the threads on the container exteriorare nicked, then they cut into the internal wall or the threads of theplastics screw closure 3. The moment required for further turning of theclosure thus increases steeply, to such an extent that the predeterminedmaximum value M3 is exceeded.

If in the course of continued rotation of the closure cone 5 up toattaining the predetermined angle of rotation W, the maximum value ofthe desired application moment M3 is exceeded, then this can also be dueto the internal thread being damaged in the course of its continuedextent inside of the screw closure 3. Because of this the cap or closurecannot be screwed on sufficiently far, so that the seal provided theredoes not come into adequate engagement with the mouth region of thecontainer 1. An internal pressure existing in the container can easilyescape. Therefore in such a case a signal is also issued through thecontrol line S of the control arrangement 19, so that this container isseparated out of the closing installation. In addition each time whenthe maximum moment M3 is exceeded prior to the predetermined angle ofrotation W being reached, the switching arrangement 11 is actuated insuch a way through the control line 23, that the motor 9 no longerdrives the closing cone 5. This prevents applying an excessively largetorque to the mouth area of the container 1 and that consequently damageoccurs.

Finally the maximum tightening moment M3 could be exceeded also prior toreaching the desired angle of rotation W, if the closure or cap 3 tiltson the thread of the container after the application moment M1 has beenreached. On the one hand it would also not be assured in that case, thatthe seal disposed in the cap seals the container pressure in a tightmanner, on the other hand, if the closure process is continued becauseof the tilting, an excessive moment can come to act on the mouth regionof the container and cause damage.

A differential member 25 is provided here within the control arrangement19, which determines the chronological derivation of the output signalof the torque sensor 15 but also of the output signal of the angle ofrotation sensor 17.

From an excessively large chronological change of the angle of rotationdetermined by this differential member 25, it can for instance also bedetermined when the closure cone 5 suddenly spins or races, that thusscrew cap closure 3 is no longer supported on the container 1. This canfor instance occur if the side wall of the cap has split or if thethread of the container has failed. In such a case a signal is issuedthrough the control S and the container involved is separated out.

If it is seen that the increase of the torque after reaching theapplication moment M1 and prior to reaching the desired angle ofrotation W is too small, then one can draw therefrom the conclusion,that either the seal in the cap is defective, that the cap was fracturedalready prior to the application onto the container or that the bottlethread was inaccurately shaped. In any case one can draw the conclusiontherefrom, that the cap will race or spin on the container. In this casealso the corresponding container is separated out by a signal in thecontrol line S.

If on the other hand the torque rises too rapidly after the applicationmoment M1 has been reached, and prior to reaching the desired angle ofrotation W, then one can conclude therefrom, that damage has occurred atthe thread of the cap or the container or that the cap or closure hastilted on the container. In this case also a signal is issued throughthe control line S and the appropriate container is separated out.

Because a maximum torque M3 is preset for the closure process, theopening moment Mo required for initial opening of the container can beadjusted to a desired value. On the other hand additional security isachieved thereby by being able to recognize tilting of the cap or damageto the thread of the cap or the container and being able to separate outthe container involved.

Since the torque and on the other hand the angle of rotation afterreaching a predetermined application moment can be preset, the momentsoccurring during closure of a container by a screw closure or cap can belimited. On the one hand damages to the mouth of the container areexcluded thereby, on the other hand overloading the closing device isexcluded, so that its wear is reduced to a minimum. The useful life ofthis mechanism is therefore greatly increased.

The method can be modified inasmuch as the screw closure 3 is screweddown by the motor 9 for as long, until reaching a torque limit value Mgis registered by the torque sensor 15 and the comparator 21, which limitvalue lies above the closure moment M2.

Due to the increased tightening moment containers 1 with slight threaddamage can also be securely sealed or closed. Basically it has to bestated, that in case of damage to the thread the closing moment M2desired in the final analysis is already reached prior to the cap havingassumed a final position on the thread of the container, becauseadditional frictional forces are built up due to the damage.

Also when using caps with a warranty or safety ring intended to indicatethe initial opening of the closure, frequently the final desired closingmoment M2 is already reached prior to the cap having assumed its finalposition on the container, because the warranty or safety ring producesan additional frictional moment. Therefore when such closures are used atorque must be applied to begin with which exceeds the final desiredclosing moment M2.

Finally an optimum contact pressure of the seal against the mouth areaof the container is also achieved by the increased tightening moment.Thereby the seal espouses the mouth in such a way that, even if theslight damage is present, an optimum sealing of the container is assuredeven if the contents of the said container are subjected tooverpressure.

In order to avoid that excessive opening moments are set up by closingwith an increased tightening moment, a reversal of the energy suppliedto the motor 9 is achieved after screwing down the cap up to thelimiting moment Mg, this by means of a control signal in the controlarrangement 19 which is fed to the switching arrangement 11 through theline 23. The motor then reverses its direction of rotation. At the sametime the angle of rotation sensor 17 is activated by this controlsignal. Its output signals are compared in the comparator 21 with anangular value W1 allocated to the left-hand rotation or the openingmotion. As soon as the preset angle of rotation lying for instance inthe range of 10° to 15° is achieved as soon as the actual angle ofrotation thus reaches the limit value W1 present in the comparator 21,the switching arrangement 11 is controlled in such a way by a controlsignal of the control device 19 through the control line 23, that theenergy supplied to the motor 9 is interrupted. Thereby the openingmotion of the cap 3 is terminated.

It is determined by tests how far the screw closure or cap must beturned in opposite direction after it has been screwed down up to thelimiting moment Mg, until the desired opening moment Mo is set up. Therequired angle of rotation can depend upon the combination of thematerials selected for the container, cap and seal.

Because the switching arrangement 11 can be activated in such a way,that an energy reversal or a pole reversal of the energy supply to themotor 9 is achieved, it is possible that the rotary device of the typedescribed above is controlled in such a way, that in case of a defectoccurring during the closure process of a container to begin with areversal of rotation is performed and the cap is again unscrewed fromthe container. Then the closing process is started anew. If now anorderly regular closing process is to be set up, the container is leftin the normal manufacturing process. Only if a discrepancy occurs again,for instance because the cap or the mouth area of the container areruined, is the container mustered out of the process. Removals can inthis way be reduced to a minimum; such removals entail that additionalprocessing steps must be performed outside of the normal work sequence.Thus an additional improvement of the closing process can be achieved byreversal of the energy supply.

By the availability of the energy reversal it is also possible to turnthe cap 3 counter to the closing direction after the first setup on thecontainer 1. In this way an optimum alignment of the thread provided inthe cap with respect to the container thread can occur. After a certainleft-hand rotation the cap snaps onto the container, which for instancecan be determined by an axial motion of the cap with the respect to thecontainer occurring. This motion can be probed by a suitable travelsensor.

The rotation of the cap counter to the closing direction results withscrew closures with a warranty- or safety-ring in that said ring isaligned in an optimal manner. This avoids jamming of the safety ringduring the subsequent screw-down of the cap.

We claim:
 1. A slewing device for screw closures for containers,comprising:a screw closure receiving member; a drive for rotating saidreceiving member; and control means for controlling power supply to saiddrive, said control means including:a torque sensor for sensing aninstantaneous drive torque; comparator means for comparing theinstantaneous drive torque with a closing torque having a predeterminedvalue; and a sensor for sensing an angle of rotation of said receivingmember and actuatable only upon the instantaneous drive torque reachingthe predetermined value.
 2. A slewing device according to claim 1,wherein said torque sensor comprises at least one of a current sensorand a voltage sensor forming part of a power supply circuit for saiddrive.
 3. A slewing device according to claim 1, further comprising apower reversal circuit associated with said control means.
 4. A slewingdevice according to claim 3, wherein said torque sensor is associatedwith said power reversal circuit.
 5. A method of placing a screw closureon a container, comprising the steps of:applying a drive torque to thescrew closure to screw it down onto the container; sensing aninstantaneous drive torque applied to the screw closure; comparing theinstantaneous drive torque with a closing torque having a predeterminedvalue; and sensing an angle of rotation of the screw closure only uponthe instantaneous drive torque reaching the predetermined value of theclosing torque.
 6. A method according to claim 5, wherein said drivetorque sensing step includes sensing at least one of a current and avoltage of power supply for driving the screw closure.
 7. A methodaccording to claim 5, further comprising the step of rotating the screwclosure, after the enclosing torque of a predetermined value is reached,a predetermined angular amount.
 8. A method according to claim 5,further comprising the step of determining a chronological change of theclosing torque.
 9. A method according to claim 5, wherein said step ofsensing an angle of rotation includes comparing an instantaneous angleof rotation with a predetermined angle of rotation.
 10. A methodaccording to claim 5, further comprising the steps of reversal of powersupply, and determining an opening moment as soon as a rotational angleof the screw closure exceeds 0°.
 11. A method according to claim 5,further comprising the steps of selecting the predetermined closingtorque as a limiting torque exceeding a desired closing torque, androtating the screw closure through a predetermined angle counter aclosing direction when the limiting torque is reached.
 12. A methodaccording to claim 5, further comprising the step of initiating anadditional closing process upon a determination of at least one of adefective angular value and a defective torque value.
 13. A methodaccording to claim 5, further comprising the step of sorting out acontainer upon sensing at least one of a defective angular value and adefective torque value.